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Internet Engineering Task Force                            P. Bryan, Ed.
Internet-Draft                                                 ForgeRock
Intended status: Informational                          February 4, 2012
Expires: August 7, 2012


             A Convention for HTTP Access to JSON Resources
                   draft-pbryan-http-json-resource-01

Abstract

   This document codifies a convention for accessing JSON
   representations of resources via HTTP.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 7, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.






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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Resources  . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   4.  Version Control  . . . . . . . . . . . . . . . . . . . . . . .  3
   5.  Operations . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     5.1.  Create . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     5.2.  Read . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     5.3.  Update . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     5.4.  Delete . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     5.5.  Patch  . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     5.6.  Query  . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     5.7.  Action . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   6.  Request Context  . . . . . . . . . . . . . . . . . . . . . . . 10
   7.  Access Control . . . . . . . . . . . . . . . . . . . . . . . . 10
   8.  Resource Validation  . . . . . . . . . . . . . . . . . . . . . 10
   9.  Resource Metadata  . . . . . . . . . . . . . . . . . . . . . . 10
     9.1.  Header . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     9.2.  Object Members . . . . . . . . . . . . . . . . . . . . . . 11
   10. Error Response . . . . . . . . . . . . . . . . . . . . . . . . 11
     10.1. Members  . . . . . . . . . . . . . . . . . . . . . . . . . 11
   11. Modifying a Resource Identifier  . . . . . . . . . . . . . . . 11
   12. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   13. Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   15. Normative References . . . . . . . . . . . . . . . . . . . . . 12
   Appendix A.  Examples  . . . . . . . . . . . . . . . . . . . . . . 13
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13






















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1.  Introduction

   JavaScript Object Notation (JSON) [RFC4627] is a common format for
   the exchange and storage of structured data.  Hypertext Transfer
   Protocol (HTTP) [RFC2616] is a common protocol for providing remote
   access to resources.

   This document codifies a convention for accessing JSON
   representations of resources via HTTP.  This promotes a common remote
   access interface across multiple disparate resources and reuse of
   conforming server and client software components.


2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   This document expresses the structure of Request-URIs in examples
   using [URI-Template] syntax.


3.  Resources

   A resource accessed through this convention is represented as a JSON
   value with an "application/json" (or derivative) Internet media type.

   An accessible resource is a member of a collection of resources.  A
   collection of resources MUST have a unique location, which is
   expressed as a part of the Request-URI of HTTP requests.  The server
   implementation determines the location of a resource collection.

   Each resource MUST have a unique identifier within a collection.  The
   server implementation MAY establish restrictions on identifiers that
   can be used, and reject requests that have identifiers that do not
   conform with a 403 Forbidden status code.


4.  Version Control

   A server MAY implement version control for resources, and use it as
   the basis of an optimistic concurrency control mechanism.  If version
   control is implemented for a given resource, the server MUST expose
   the resource version in responses, and clients MUST use preconditions
   when performing operations that modify such resources.

   If a server implements version control for a resource, and the



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   resource version is incorrectly specified by a client for an
   operation that modifies the resource, the server SHOULD indicate this
   with a 412 Precondition Failed status code.

   If a server implements version control for a resource and the
   resource version is not specified by a client for an operation that
   modifies the resource, the server SHOULD indicate this with a 428
   Precondition Required status code, per [New-Status].

   The server implementation determines how a resource version is
   computed; it MUST ensure that different values for a given resource
   compute different versions.  Clients SHOULD treat a resource version
   provided by a server as opaque.

   The server expresses resource version via the "ETag" response header
   and the "_rev" metadata member in JSON object entity responses.  The
   client expresses resource version via the "If-Match" and "If-None-
   Match" precondition request headers.


5.  Operations

   This convention provides a uniform set of operations, all of which
   are implemented via standard HTTP methods.  The operations are:
   create, read, update, delete, patch, query, and action.  The server
   implementation MAY conditionally implement any operation.

5.1.  Create

   The "create" operation allows a client to create a new resource in a
   collection.  A resource is created in one of two ways: if the client
   is requesting a specific identifier, then the resource is created via
   the HTTP PUT method; if the server is to select its own identifier,
   then the resource is created via the POST method.  The PUT method
   SHOULD be preferred over POST.

5.1.1.  PUT Request

   In the PUT method, the identifier of the resource to create is
   specified in the Request-URI of the HTTP request.  The server MAY
   override the requested identifier of the resource and select a
   suitable identifier of its own.

   To unambiguously request resource creation, the "If-None-Match"
   header MUST contain the value "*".  If no precondition header
   unambiguously requests resource creation or update, the server MAY
   use its own means of determining how to interpret the PUT method.




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   PUT /{collection}/{id} HTTP/1.1
   Content-Type: application/json
   If-None-Match: *
   ...

   [JSON representation of resource to create]

5.1.2.  POST Request

   In the POST method, the identifier of the resource is not specified.
   The Request-URI of the request MUST NOT contain a query component, in
   order to distinguish it from the "action" operation.  The server MUST
   select a suitable identifier for the created resource.

   POST /{collection} HTTP/1.1
   Content-Type: application/json
   ...

   [Resource representation]

5.1.3.  Response

   HTTP/1.1 201 Created
   Content-Type: application/json
   Location: [location of resource]
   ETag: "[resource version]"
   ...

   [Resource metadata object]

   The "Location" header field contains a URI that identifies the newly
   created resource.  The optional "ETag" header field contains the
   version of the newly created resource.  The resource metadata object
   also contains the identifier and optional version of the newly
   created resource.

   If version control is implemented for a given resource, the server
   MUST expose the new resource version in the ETag header of the
   response.

5.2.  Read

   The "read" operation allows a client to read a representation of a
   resource from the server.  It is implemented using the HTTP GET
   method.  The client MUST NOT include a query component in the
   Request-URI, in order to distinguish it from the "query" operation.

   If the resulting representation of the resource is a JSON object, it



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   SHOULD contain the JSON "_id" member, and also the "_rev" member if
   resource version is supported by the server implementation.

5.2.1.  Request

   GET /{collection}/{id} HTTP/1.1
   ...


5.2.2.  Response

   HTTP/1.1 200 OK
   Content-Type: application/json
   ETag: "[resource version]"
   ...

   [Resource representation]

   If version control is implemented for a given resource, the server
   MUST expose the resource version in the ETag header of the response.

5.3.  Update

   The "update" operation allows a client to update the representation
   of a resource on the server.  It is performed using the HTTP PUT
   method.  To cause the PUT method to unambiguously request a resource
   update, the "If-Match" header MUST contain the current version of the
   resource.  If no precondition header unambiguously requests resource
   creation or update, the server MAY use its own means of determining
   how to interpret the PUT method.

5.3.1.  Request

   PUT /{collection}/{id} HTTP/1.1
   Content-Type: application/json
   If-Match: "[resource version]"
   ...

   [Resource representation]












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5.3.2.  Response

   HTTP/1.1 200 OK
   Content-Type: application/json
   ETag: "[resource version]"
   ...

   [Resource metadata object]

   If version control is implemented for a given resource, the server
   MUST expose the updated resource version in the ETag header of the
   response.

5.4.  Delete

   The "delete" operation allows a client to delete a resource, or
   optionally an entire collection of resources.  It is performed using
   the HTTP DELETE method.

   To delete a single resource, both the collection location and
   resource identifier MUST be specified in the Request-URI of the HTTP
   request.  To delete an entire collection, only the collection
   location MUST be specified.

5.4.1.  Request

   DELETE /{collection}/{id} HTTP/1.1
   If-Match: "[resource version]"
   ...


5.4.2.  Response

   HTTP/1.1 204 No Content
   ...

5.5.  Patch

   The "patch" operation allows a client to apply a set of partial
   modifications to a resource on the server.  This is particularly
   useful if the client is provided with redacted representations of
   resources and/or does not have permission to modify resources in
   their entirety.

   The "patch" operation is performed using the HTTP PATCH method, per
   [RFC5789].  The supported patch document format(s) to apply the
   partial modifications is determined by the server implementation.




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5.5.1.  Request

   PATCH /{collection}/{id} HTTP/1.1
   Content-Type: application/json-patch
   If-Match: "[resource version]"
   ...

   [JSON Patch document]

5.5.2.  Response

   HTTP/1.1 200 OK
   Content-Type: application/json
   ETag: "[resource version]"
   ...

   [Resource metadata object]

   If version control is implemented for a given resource, the server
   MUST expose the updated resource version in the ETag header of the
   response.

5.6.  Query

   The "query" operation performs a parametric query of a resource or
   collection, and responds with a result.  The execution of a query
   MUST NOT incur side effects.  It is implemented using the HTTP GET
   method.  The client MUST include a query component in the Request-URI
   to distinguish it from the "read" operation.

   To query a single resource, both the collection location and resource
   identifier MUST be specified in the Request-URI of the HTTP request.
   To query an entire collection, only the collection location MUST be
   specified.

5.6.1.  Request

   GET /{collection}/{id}?{query} HTTP/1.1
   ...












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5.6.2.  Response

   HTTP/1.1 200 OK
   Content-Type: application/json
   ...

   [JSON query result value]

   The structure of the query result value is determined by the server
   implementation.

5.7.  Action

   The "action" operation performs a parametric action on a resource or
   collection, and responds with an optional result.  The execution of
   an action MAY incur side effects.

   The operation is implemented via the HTTP POST request.  The Request-
   URI MUST NOT contain a query component, in order to distinguish it
   from a "create" operation.  The request MAY include an entity body.

   To perform an action on a single resource, both the collection
   location and resource identifier MUST be specified in the Request-
   URI.  To perform an action on an entire collection, only the
   collection location MUST be specified.

   If the response contains a result value, then the server SHOULD
   respond with a 200 OK status code; otherwise it SHOULD respond with a
   204 No Content status code.

5.7.1.  Request

   POST /{component}/{id}?{query} HTTP/1.1
   Content-Type: application/json
   ...

   [Optional JSON value]

5.7.2.  Response

   HTTP/1.1 200 OK
   Content-Type: application/json
   ...

   [JSON action result value]

   The structure of the action result value (if any) is determined by
   the server implementation.  If version control is implemented for a



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   given resource, the server MAY expose the updated resource version in
   the ETag header of the response.


6.  Request Context

   A server MAY require some form of request context be established by
   the client prior to allowing access to resources.  How such context
   is established, persisted and transmitted is out of the scope of this
   convention, and SHOULD be specified by the server implementation.

   If inadequate request context has been established, the server SHOULD
   indicate this with a 401 Unauthorized error status code, unless there
   is another means of indicating such which is consistent with the
   required request context.


7.  Access Control

   The server implementation MAY enforce access control policies that
   restrict what resources a client can access and/or on what JSON
   values within each resource may be accessed.

   If the necessary context has been established (including no context
   at all) but such context does not permit the requested access to a
   resource, the server SHOULD indicate this with a 403 Forbidden error
   status code and a detail message describing the nature of the access
   denial.

   The server implementation MAY amend representations of resources to
   conform to access control policies, and SHOULD specify under what
   conditions such amendments are applied.


8.  Resource Validation

   The server MAY enforce validation rules on resource representations
   provided by the client.  If such a validation fails, the server
   SHOULD indicate this with a 403 Forbidden error status code and a
   detail message describing the nature of the validation failure.


9.  Resource Metadata

   Most responses to requests contain metadata about the resource being
   accessed.  The metadata is included an HTTP ETag response header as
   well as members within a JSON object resource representation,
   including a JSON object specifically intended to contain only



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   metadata (referred to within this document as a "resource metadata
   object").

9.1.  Header

   ETag
   The current version of a resource, if version control is implemented
   for the resource.

9.2.  Object Members

   "_id": string, required
   The identifier of the resource, relative to the collection it is a
   member of.

   "_rev": string, optional
   The current version of the resource, if version control is
   implemented for the resource.


10.  Error Response

   In the event of an error, a 4xx or 5xx HTTP status code SHOULD BE
   expressed in the response, with an entity body containing an error
   object adhering to the following structure:

   {
       "error": number,
       "reason": string,
       "detail": string
   }

10.1.  Members

   "error": number, required
   The value provided SHOULD coincide with the status code provided in
   the HTTP response.

   "reason": string, optional
   A short reason phrase of the error.

   "detail": string, optional
   The detail message of the error.


11.  Modifying a Resource Identifier

   The server MAY allow the update and/or patch operations to modify the



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   identifier of a resource within the collection if the resource has a
   JSON object representation.  If such modification is disallowed, the
   server SHOULD respond with a 403 Forbidden status code.

   To indicate a request to modify the resource identifier, the "_id"
   metadata member should be included in the request entity and differ
   from the existing resource identifier in the Request-URI.

   If the server successfully modifies the resource identifier, instead
   of responding with a 200 OK status code, the server MUST respond with
   a 201 Created status code, with a Location header containing the URI
   of the newly created resource.

   If there is already a resource with the requested identifier, the
   server MUST respond with a 409 Conflict status code indicating it
   could not be modified.  If the server rejects the identifier as
   invalid, the server SHOULD respond with a 403 Forbidden status code.


12.  IANA Considerations

   This document has no IANA actions.


13.  Security Considerations

   TBD.


14.  Acknowledgements

   The following individuals contributed ideas, feedback and wording,
   which contributed to the content of this specification:

      Alin Brici, Andi Egloff.

   This convention was influenced by various projects that expose HTTP-
   based access APIs, especially those that managed JSON-based
   representations, notably CouchDB.


15.  Normative References

   [New-Status]
              Nottingham, M. and R. Fielding, "Additional HTTP Status
              Codes", October 2011, <http://tools.ietf.org/html/
              draft-nottingham-http-new-status-03>.




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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627, July 2006.

   [RFC5789]  Dusseault, L. and J. Snell, "PATCH Method for HTTP",
              RFC 5789, March 2010.

   [URI-Template]
              Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
              and D. Orchard, "URI Template", September 2011,
              <http://tools.ietf.org/html/
              draft-gregorio-uritemplate-07>.


Appendix A.  Examples

   TBD.


Author's Address

   Paul C. Bryan (editor)
   ForgeRock

   Phone: +1 604 783 1481
   Email: pbryan@anode.ca



















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